1. Field of the Invention
This invention relates to a shock absorber adapted to support a bumper reinforcement member on a body member of a vehicle.
2. Description of the Related Art
A shock absorber adapted to absorb an impact exerted on a bumper reinforcement member is used as a member for supporting the bumper reinforcement member on a body member. When the bumper reinforcement member is bent in a projecting state frontward in the length direction of the vehicle, an impact received by the bumper reinforcement member is exerted on the shock absorber in the diagonal direction thereof to cause the shock absorber to be inclined. When the shock absorber is of the type which absorbs impact energy owing to the plastic deformation thereof, the impact energy cannot be absorbed satisfactorily due to an inclination of the shock absorber.
Regarding this point, a shock absorber (Halteglied) disclosed in the German Patent No. 3711692 is joined to a bumper reinforcing member (Stoxcex2stange) with a predetermined degree of freedom provided in a horizontal plane but a general construction of the shock absorber becomes complicated. In view of this, a bumper reinforcement member of the invention disclosed in JP-A-2001-158312 is provided with an engagement portion, which is engaged with an outer end portion of a shock absorber (or a shock absorbing member) when a collision of a vehicle occurs in which the bumper reinforcement is displaced in the length direction of the vehicle, for the purpose of preventing a cost increase caused by the complication of the general construction of the shock absorber, and eliminating a scatter of a shock absorbing performance occurring due to, especially, an inclining movement of the shock absorber in the outward direction of the vehicle. Furthermore, a flat plate type bumper stay is laid between the bumper reinforcement and a body member so that the bumper stay holds the shock absorber (or the shock absorbing member) therebetween.
Although the construction of the invention disclosed in JP-A-2001-158312 is certainly simple as compared with that of the invention disclosed in the German Patent No. 3711692, the impact energy is also absorbed in the flat plate type bumper stay the shock absorbing performance of which is hard to predict, so that a new problem arises, i.e., a stable shock absorbing performance is difficult to be obtained. However, when the bumper stay is not provided, there is the possibility that an outer end portion of the""shock absorber (or the shock absorbing member) which is distant from the engagement portion provided on the bumper reinforcement be not engaged well with the engagement portion. When the outer end portion of the shock absorber is not engaged well with the engagement portion of the bumper reinforcing member, the inclining of the shock absorber necessarily occurs.
The shock absorber disclosed in JP-A-2001-158312 is provided with a bead which permits the bumper stay to be bent so that the bumper stay does not disturb the shock absorber (shock absorbing member) from absorbing an impact. In this case, however, another problem arises in that the bumper stay flares the bumper reinforcement in the vertical direction. Especially, in the bumper reinforcement of a cross-sectionally opened structure disclosed as an example in JP-A-2001-158312, it may suddenly decrease section modulus of the bumper reinforcement opened vertically.
Therefore, a shock absorber capable of displaying a necessary and sufficient shock absorbing performance without being inclined even when the axial direction of the shock absorber is inclined outward with respect to the width direction of a vehicle and crosses the bumper reinforcing member at the right angles thereto.
The shock absorber according to the present invention is adapted to support a bumper reinforcing member of a vehicle and absorb by the plastic deformation of the shock absorber an impact exerted on the bumper reinforcing member, the shock absorber comprising a first collapsible shock absorbing part, and a second shock absorbing part to be compressed in the axial direction thereof inclined outward in the width direction of the vehicle, the first shock absorbing part having a structure of a basin-like truncated conical shape and including a skirt-shaped side surface, a top surface surrounded by a smaller-diameter-side circumferential edge of the side surface, an annular flange surface projecting from a larger-diameter-side circumferential edge of the side surface in the radially outward direction, and a bead integrally formed on the side surface in connection between the larger-diameter-side circumferential edge and the smaller-diameter-side circumferential edge, whereby the shock absorber has a function of aligning a direction in which the impact exerted on the bumper reinforcing member with the axial direction of the second-shock absorbing part while absorbing the same impact, and the second shock absorbing part having a function of absorbing an impact transmitted from the first shock absorbing part.
The first shock absorbing part may have a structure of a basin-like truncated pyramid shape, and preferably a structure of a basin-like truncated conical shape. When the first shock absorbing part has a polyhedral conical shape or a truncated conical shape, a collapse of the side surface except a bead-formed part thereof becomes substantially uniform in the circumferential direction, so that a designed shock absorbing performance can be displayed. In this first shock absorbing part, the top surface is brought into contact with a front end of the second shock absorbing part with the top surface faced rearward with respect to the length direction of a vehicle, or the flange surface is brought into contact with the front end of the second shock absorbing part with the top surface faced frontward with respect to the length direction of the vehicle.
The second shock absorbing part serves the purpose as long as this shock absorbing part is compressed axially and absorbs an impact. The second shock absorbing part may be of a cylindrical structure, and preferably of a multistage tubular structure in which a smaller-diameter tube portion and a larger-diameter tube portion formed by partially reducing or partially increasing the diameter of a straight tube, and which are connected together via a stepped portion in which boundary regions of the smaller-diameter and larger-diameter tube portions are folded back into each other to put these tube sections in a previously absorbed state. In this embodiment, the first shock absorbing part is formed by bringing the top surface thereof into contact with a front end of the smaller-diameter tube portion of the second shock absorbing part with the top surface faced rearward with respect to the length direction of a vehicle, or by bringing the annular flange surface thereof into contact with the front end of the smaller-diameter tube portion of the second shock absorbing part with the top surface faced forward with respect to the length direction of the vehicle.
In the shock absorber according to the present invention, a shock transmission direction is corrected by a collapse of the first shock absorbing part, and the inclination of the second shock absorbing part is thereby prevented. Thus, the second shock absorbing part being collapsed in the initial inclined axial direction. For example, when the bumper reinforcing member is bent forward in a projecting state in the length direction of the vehicle, a shock causes the bumper reinforcing member to be deformed so that the radius of bend thereof becomes smaller, and the deformation of this bumper reinforcing member gives the second shock absorbing part a force for inclining the second shock absorbing part outward in the width direction of the vehicle. In the first shock absorbing part, the rigidity of an outer side in the width direction of the vehicle of the side surface is set higher than that of an inner side in the width direction of the vehicle of the side surface owing to the bead formed on the outer side in the width direction of the vehicle of the side surface. According to this structure, the side surface of the first shock absorbing part collapses a little at the outer side in the width direction of the vehicle, and, conversely, much at the inner side in the width direction of the vehicle. The first shock absorbing part having different quantities of collapse at the inner and outer sides thereof with respect to the width direction of the vehicle corrects the shock transmission direction so that the shock transmission direction is aligned with the axial direction of the second shock absorbing part, to thereby prevent the inclining of the second shock absorbing part.
The outward inclination of the axis of the shock absorber in the width direction of the vehicle occurs when the shock absorber supports the bumper reinforcing member at right angles to a contact surface thereof with respect to the bumper reinforcing member bent forward in a projecting state in the length direction of the vehicle. Even when the bumper reinforcing member is formed straight with the axial direction of the shock absorber inclined either inward or outward with respect to the width direction of the vehicle, the present invention can be applied to the shock absorber.
Concretely, the direction in which the second shock absorbing part is inclined is; (1) a direction in which a crossed axes angle (which will hereinafter be referred to as a bumper crossed axes angle) oh the front side with respect to the length direction of the vehicle and formed between a tangential direction of the bumper reinforcing member and the axial direction of the shock absorber is smaller than 90 degrees; or (2) a direction in which a crossed axes angle (which will hereinafter be referred to as a vehicle crossed axes angle) on the front side in the length direction of the vehicle and formed between the width direction of the vehicle and the axial direction of the shock absorber is smaller than 90 degrees. In view of this, the setting of different quantities of collapse of the first shock absorbing part with a bumper crossed axes angle not 90 degrees (not having orthogonally crossed relation) may be done by providing a bead on the side on which the shock absorber is inclined toward the side having a bumper crossed axes angle of smaller than 90 degrees. The setting of different quantities of collapse of the first shock absorbing part with a vehicle crossed axes angle not 90 degrees (not having orthogonally crossed relation) may be done by providing the bead on the side on which the shock absorber is inclined toward the side having a vehicle crossed axes angle of smaller than 90 degrees. In the shock absorber supporting the bumper reinforcing member which is bent forward in a projecting state in the length direction of the vehicle, the inclination of the second shock absorbing part occurs generally outward in the width direction of the vehicle, and the bead is therefore provided on the outer side in the width direction of the vehicle of the side surface of the first shock absorbing part. However, when the above-mentioned condition is met, the bead may be provided on the inner side in the width direction of the vehicle of the side surface of the first shock absorbing part.
More concretely, the first shock absorbing part includes a bead integrally provided on the side surface thereof and having a cross-sectionally triangular shape, an opening angle within the range of plus or minus 45 degrees in the circumferential direction of the top surface at a center line extending outward from the center of the top surface in the width direction of the vehicle, and extends in connection between the larger-diameter-side circumferential edge and the smaller-diameter-side circumferential edge. When the angle at which the cross-sectionally triangular bead extends exceeds plus minus 45 degrees in the circumferential direction around the width direction of the vehicle as the center, the improvement of rigidity of the first shock absorbing part due to the existence of the bead extends over the whole of the first shock absorbing part, so that a difference in rigidity, in its turn, a difference in the degree of a collapse of the inner and outer side sections of the first shock absorbing part in the width direction of the vehicle does not occur. This inconvenience will be described in relation to the size of the top surface of the first shock absorbing part. That is, a first shock absorbing part includes a bead integrally provided on a side surface thereof and having a cross-sectionally triangular shape, an opening side length within the range of 0.1 to 0.7 times as large as a diameter of the top surface at a center line extending outward from the center of the top surface in the width direction of the vehicle, and extends in connection between the larger-diameter-side circumferential edge of a first shock absorbing part and the smaller-diameter-side circumferential edge thereof. Strictly speaking, 0.7 times the diameter of the top surface is equal to 1/root 2 thereof, i.e. a sine value at an angle of 45 degrees. In addition, 0.1 times the diameter of the top surface represents a lower limit value at which a normal bead molding operation can be carried out.
Instead of the cross-sectionally triangular bead, a cross-sectionally sector-shaped bead may be used. Namely, the first shock absorbing part is integrally provided on the side surface thereof with a bead having a cross-sectionally sector having an opening angle within the range of plus or minus 45 degrees in the circumferential direction of the top surface at a center line extending outward from the center of the top surface in the width direction of the vehicle, and extends in connection between the larger-diameter-side circumferential edge and the smaller-diameter-side circumferential edge. The first shock absorbing part may also be integrally provided on a side surface thereof with a bead having a cross-sectionally sector having an opening side length within the range of 0.1 to 0.7 times as large as a diameter of the top surface at a center line extending outward from the center of the top surface in the width direction of the width of the vehicle, and extends in connection between the larger-diameter-side circumferential edge of the first shock absorbing part and the smaller-diameter-side circumferential edge thereof.
When the shock absorber according to the present invention supports a bumper reinforcing member of a cross-sectionally closed structure having a front surface and a rear surface, the following three support structures can be exemplified.
(a) A structure formed by connecting an annular flange surface of a first shock absorbing part to a front surface of a bumper reinforcing member, connecting a top surface of the first shock absorbing part to a front end of a smaller-diameter tube portion of a second shock absorbing part, and connecting a rear end of a larger-diameter tube portion of the second shock absorbing part to a front portion of a body member, (b) a structure formed by connecting the annular flange surface of the first shock absorbing part to the front surface of the bumper reinforcing member, connecting a side surface of the smaller-diameter tube portion of the second shock absorbing part to a rear surface of the bumper reinforcing member, bringing the top surface of""the first shock absorbing part and a front end of the smaller-diameter tube portion of the second shock absorbing part into contact with each other, and connecting the rear end of the larger-diameter tube portion of the second shock absorbing part to the front portion of the body member, and (c) a structure formed by bringing the annular flange surface of the first shock absorbing part into contact with the front surface of the bumper reinforcing member, connecting the top surface of the first shock absorbing part to the front end of the smaller-diameter tube portion of the second shock absorbing part, connecting the side-surface of the smaller-diameter tube portion of the second shock absorbing part to the rear surface of the bumper reinforcing member, and connecting the rear end of the larger-diameter tube portion of the second shock absorbing part to the front portion of the body member. Bolts may be used for each part to be connected, and a welding method may also used when the parts need to be connected firmly.
The first shock absorbing part having a structure of a basin-like truncated conical shape is easily collapsed as compared with the second shock absorbing part of a cylindrical or a multistage tubular structure. Therefore, the first shock absorbing part is collapsed when such a low-speed collision of a vehicle occurs that does not cause the second shock absorbing part to be plastically deformed, to absorb an impact. When a high-speed collision of the vehicle occurs, the first shock absorbing part is collapsed to absorb an impact, while correcting an impact transmission direction. The second shock absorbing part is then compressed to absorb the impact.
Thus, in the shock absorber according to the present invention, the first shock absorbing part is collapsed to absorb an impact when a low-speed collision of a vehicle occurs at which time the second shock absorbing part is not compressed. When a high-speed collision occurs, the first shock absorbing part is collapsed while correcting a shock transmission direction, and thereby the second shock absorbing part can be compressed without being inclined. This enables a required and sufficient shock absorbing performance of the shock absorber to be displayed in a range of a low-speed collision of the vehicle to a high-speed collision thereof.
Further, the shock absorber according to the present invention is not required to have a bumper stay additionally. Even when the present invention is applied to a bumper reinforcing member of a cross-sectionally opened structure, sudden drop of section modulus thereof can be avoided.
Besides these, the first shock absorbing part is fixed previously to the bumper reinforcing member or to a fixing aid, so that the second shock absorbing part connected to or engaged with the first shock absorbing part can be positioned with respect to the bumper reinforcing member. This causes the improvement of the assembling efficiency to the shock absorber.